The present invention relates to industrial vehicles, and more particularly, to a vehicle requiring an overhead support, such as for tilt cylinders in a heavy duty forklift vehicle.
In industrial vehicles, it is sometimes necessary to provide overhead structural support for an attachment. For example, in the forklift vehicle environment, it is recognized that there is an advantage to provide overhead tilt cylinders for the front mounted, forklift attachment. With the overhead cylinders, better control of the tilting of the attachment can be achieved. The overhead positioning of the cylinders allows the piston rod to be attached to an intermediate point along the support structure of the vertically extending forklift attachment. This provides a better point of attachment in that the cylinder can be mounted substantially horizontally, and thus provide superior force application.
This is particularly important in operation of the cylinders to tilt the forklift attachment toward or away from the vehicle as heavy loads are lifted, especially from high, overhead positions. If the cylinders are mounted low on the deck of the vehicle, it requires greater pulling/pushing power (because of the reduced effective lever arm) to tilt the forklift attachment under the same loading. Positioning the cylinders overhead provides better control, since less power is required and better stability as the vehicle is moved, especially with the load in the overhead position.
A side benefit of overhead cylinder mounting is that there is provided falling object protective structure (FOPS) without providing additional, unnecessary passive structure, that would otherwise simply add cost and weight to the vehicle. The supporting structure for the overhead cylinders performs the secondary FOPS function adding substantially to the cost/benefit ratio for the vehicle.
In the past, the manufacturers have relied generally on providing a singular, generally vertical tower support or post on each side of the vehicle for mounting the tilt cylinders. The tower supports are connected by a single, overhead cross beam with the base of the tilt cylinders being attached to the top of the towers. In terms of structural support for the cylinders and FOPS efficiency in the immediate area of the driver station, this prior arrangement has proven to be satisfactory.
However, in order to give the cylinders proper mounting support, these tower structures of the prior art have necessarily been relatively massive in size. The tower supports are fabricated of heavy gauge steel in the form of a tapering box cross section. The front of the box is designed to be substantially vertical in order to fit immediately behind the cab surrounding the driver station, with the back of the tower support being tapered from top to bottom. The cross section of the tower support is designed to be greater at the base than at the top. This is due to the increased moment of force generated by compression/tension in the overhead mounting cylinders acting on the overhead support as the load is picked up by the forks.
Also, by tapering the tower supports, the visibility to the rear and sides of the vehicle is kept as open as possible commensurate with the requirement for strength to support the cylinders. While state of the art warning devices for backing vehicles, improved driver station positioning and improved deck configurations have provided good visibility in the past, continuing to improve commensurate with good structural design is desirable. This need for still further improvement applies especially to the manner of supporting the overhead tilt cylinders, in a heavy duty forklift vehicle, as will be seen in detail below as the description of the preferred embodiment of the present invention develops.